The present invention relates generally to an illumination and imaging system for a full frame document reproduction machine and, more particularly, to a two-dimensional illumination array which provides a uniform illumination level at a document plane.
Prior art full frame document illumination and imaging systems generally employ a flash lamp or series of flash lamps combined with a projection lens to provide full frame exposure of a document at a photosensitive image plane. Representative systems are disclosed in U.S. Pat. Nos. 3,697,177 (Booth) and 4,333,723 (Green et al). These prior art systems offer relatively high throughput compared to the conventional scan/rescan systems but also have several disadvantages. The flash lamps and their power supplies and quench circuits add a significant expense to the imaging system. And, typically, a large enclosed housing with reflective interior surfaces is required to enhance efficiency, adding to the system cost.
The flash lamps used in these prior art systems are all located out of the optical path; light reaches the platen by reflection from mirrors; directly from the lamps; or indirectly from reflectors associated with the lamps. The light undergoes multiple reflections from the interior reflective walls of the illumination housing. A generally uniform level of illumination is required at the document object plane which is a transparent platen in a typical reproduction device. This uniform illumination level, in practice, has proven difficult to achieve.
The present invention is directed towards a novel illumination source to be used in a full frame imaging system defined as a system in which an image of a document is formed as a complete latent image on a photoreceptor (as opposed to scanning systems where the image is incrementally formed by a linear scan/illumination technique), which does not require the use of flash lamps. The novel illumination source need not be contained in a housing and, in fact, in a preferred embodiment, can be formed integral with the document platen. The illumination source is realized by forming a two-dimensional area array of discrete light sources in the body of a transparent substrate. The substrate has dimensions corresponding to the document sizes to be reproduced and is positioned between the document and a projection lens. The light sources are energized by an electrical power source to provide a uniform level of illumination at the document/platen interface. More particularly the invention is directed to a full frame imaging system comprising:
a transparent platen for supporting a document to be copied,
a projecting means for projecting a reflected image of the entire document onto a photoreceptor plane,
a two-dimensional illuminator array, said array positioned between said platen and said projecting means, and
means for activating said array whereby light provided by said array is directed towards, and reflected from, said document, passing through said array and projected onto said photoreceptor to form a latent image of the entire document thereon.